The present disclosure relates to fluid pressure operated rotary torque transmitting devices for use in brakes and clutches. Heretofore, fluid pressure operated clutches and brakes have typically employed a pneumatically pressurized bladder for actuating brake shoes or have employed pistons for providing pressure against friction discs; and, have typically used pneumatic pressure from available air compressors. These types of pneumatically operated brakes and clutches are limited in their power transmitting density by virtue of the limits of available air compressors which generally do not provide air pressure higher than 150 psi (1.034 MPa). Thus, for relatively high power or torque transmission, the volume or size of the brake or clutch required to provide the desired torque transmission has resulted in prohibitively large power transmission assemblies for the desired application. This has particularly been a problem for relatively large clutches/brakes capable of transmitting torque of at least one hundred eighty thousand (180,000) pound-feet (2.43×105 Newton-meters). Thus, it has been found desirable to provide fluid pressure operated brakes and clutches which may be operated with commercially available higher pressure hydraulic fluid pressure sources, thereby eliminating the cost of specialized high pressure pneumatic compressor equipment. An example of such a hydraulically operating brake or clutch which disengages upon release of the hydraulic pressure is that described in U.S. Pat. No. 4,615,418 and U.S. Pat. No. 5,383,544. Such devices thus provide for engagement in the event of loss of hydraulic fluid pressure.
However, as the annular friction discs wear in service, in the aforesaid type hydraulically operated brakes and clutches, the engagement position of the discs and reaction members or plates is shifted to a position more distant from the actuating springs. Wear thus moves the springs closer to their free length position and therefore reduces the spring force available for engagement. Heretofore, in order to maintain a desired engagement force of the springs, after significant wear of the friction discs, it has been necessary to remove the brake or clutch from service, disassemble the unit and either reposition the mounting of the springs to accommodate the wear on the friction discs or to replace the friction discs.
It has therefore been desired to provide a convenient way or means of adjusting the engagement position of the friction discs in a hydraulically operated brake or clutch assembly of the type which is disengaged by release of the hydraulic pressure without disassembly of the unit.